1. Field of the Invention
The present invention relates to a setting tool for driving fastening elements in a constructional component and including a piston guide defining a guide space having a front region and a rear region, a drive piston displaceable in the guide space by propellant gases generated by a propellant charge from its initial position in the rear region of the guide space to its end position in the front region of the guide space, and a storage space for the propellant gases and connected by a valve with the rear region of the guide space, and having an outlet communicating with the front region of the guide space.
2. Description of the Prior Art
Setting tools of a type described above can be operated with evaporated, liquid or solid fuels. In the combustion-engined and explosion-operated setting tools, the drive piston in driven during a setting process by combusted gases. The drive piston drives the fastening elements in a constructional component.
The drive piston of the setting tool should be returned in its initial position after a drive-in process in order to be able to execute a next attachment process.
German Publication DE-19547859A1 discloses a powder charge-operated setting tool in which the gases generated as a result of combustion of a propellant charge are used for returning the drive piston in its initial position.
In the setting tool of DE-19547859A1, the drive piston is displaceably supported in a guide space of a piston guide. Adjacent to the piston guide, there is provided a storage space that is connected with the guide space by an inlet channel provided with a check valve. An outlet opening connects the storage space with a setting direction end region of the guide space. During a setting process, hot, pressurized propellant or combustion gases partially flow into the storage space. After the storage space is filled, the check valve closes the inlet channel, and the stored gas flows through the outlet opening, with the piston being returned to its initial position by the internal end pressure applied by the gases.
In order to achieve a high functional reliability, a high storage pressure for a predetermined time period should be maintained. Practically, this is difficult to achieve for all operational conditions, different propellants, and different power outputs.
In conventional setting tools, because of leakage, a pressure loss occurs. The leakage occurs, among others, because of seal leakage in the bolt guide, in the gas flow, at piston head and piston stem. Also, cooling of the propellant gases in the storage space leads to loss of pressure. The cooling of the propellant gases results from a relatively large surface of the storage space which is coaxial with the piston. Also, a further drawback of this solution consists in that the propellant gas, which flows into a space in front of the piston, is compressed as a result of multiple rebounds of the drive piston which often occur, e.g., during driving of fastening element in constructional components containing steel. The compression of the propellant gas increases leakage at the bolt guide and the piston head. This results in inadequate end pressure, which leads to an incomplete displacement of the drive piston to its initial position.
Accordingly, an object of the present invention is to provide a setting tool of the type described above in which a reliable displacement of the drive piston in its initial position is insured.